Coiled or reeled tubing equipment is used in the oil and gas industry to work over existing wells. In addition, the equipment is used to drill new wells.
Coiled tubing equipment utilizes a long flexible tube. When not in use, the tubing is stored on a reel on the surface. To use the tubing, it is unwound from the reel and inserted into the well. The device that inserts the tubing into, and also removes the tubing from, the well is known in the industry as an injector.
When a length of tubing is in the well, the injector supports the tubing by a series of gripper blocks. The gripper blocks operate in pairs. Each pair has diametrically opposed gripper blocks which receive the tubing therebetween. To grip the tubing, the paired gripper blocks are forced together to clamp to the tubing. To inject the tubing into the well, the gripper blocks are moved downwardly toward the earth. To retract the tubing from the well, the gripper blocks are moved upwardly away from the earth.
The gripper blocks are forced together by skates. While the gripper blocks are able to move in a vertical direction, the skates are generally immobile in the vertical direction. The skates are therefore provided with rollers that contact the moving gripper blocks.
In prior art injectors, the skate rollers are mounted onto a fixed shaft by way of bearings that are positioned along a center line of the load. The bearings are located inside of the skate roller and consequently bear the entire load. The bearings can be a single bearing, with two sets of rollers, or two bearings, each with a single set of rollers.
A problem arises when the gripper blocks become misaligned. The gripper blocks are coupled to a chain, which chain moves the gripper blocks. The chain frequently becomes misaligned. This increases the load on the bearings, resulting in a bearing failure. When one skate roller bearing fails, the load on the other skate roller bearings increase. This in turn lead to multiple failures, requiring overhaul of the injector.
With the prior art design, an injector can be used for about one million feet of tubing before the bearings fail. If the injector is used on 25,000 feet deep wells, the injector can only be used on about 20 wells before the bearings need to be replaced. A typical injector may have 40-50 rollers. Replacing the bearings is therefore a time consuming and expensive task.